clearInterval is killing setTimeout

I got an error :

in function called from system
Uncaught Error: Unknown Timeout
at line 17 col 31

        clearTimeout(timer);

// 红外移动传感 FIR800 5v
// http://www.espruino.com/Pyroelectric
// Relay: low level trigger

function run() {
    var timer;
    var pyreolectric = A0;
    var relay = A1;
    var delay = 20000; // 20 sec

    setWatch(function () {
        console.log("Movement detected");
        LED2.write(1);
        digitalWrite(relay, 0);// trigger relay: ON

        if (timer !== undefined) {
            clearTimeout(timer); // debounce
        }

        timer = setTimeout(function () {// trigger relay: OFF
            LED2.write(0);
            digitalWrite(relay, 1);
        }, delay);
    }, pyreolectric, { repeat: true, edge: "rising" });
}
E.on('init', run);

Does the code have some mistakes ? Help, thx!